Answer:
Habituation.
Explanation:
Habituation refers to the psychological learning mechanism where the reaction to a stimulus is reduced after repeated exposure to it. This definition suggests that because of repeated exposure to it, an organism can tend to ignore a stimulus. It happens in everyday life but we still do not realize it to a large extent. As per the question, Libby doesn’t feel the pencil behind her ear as she left it there and forgot about it is an example of habituation.